Promoter hypomethylation upregulates Na⁺-K⁺-2Cl^- cotransporter 1 in spontaneously hypertensive rats

The Na⁺-K⁺-2Cl^- cotransporter 1 (NKCC1) is one of several transporters that have been implicated for development of hypertension since NKCC1 activity is elevated in hypertensive aorta and vascular contractions are inhibited by bumetanide, an inhibitor of NKCC1. We hypothesized that promoter hypomethylation upregulates the NKCC1 in spontaneously hypertensive rats (SHR). Thoracic aortae and mesenteric arteries were excised, cut into rings, mounted in organ baths and subjected to vascular contraction. The expression levels of nkcc1 mRNA and protein in aortae and heart tissues were measured by real-time PCR and Western blot, respectively. The methylation status of nkcc1 promoter region was analyzed by combined bisulfite restriction assay (COBRA) and bisulfite sequencing. Phenylephrine-induced vascular contraction in a dose-dependent manner, which was inhibited by bumetanide. The inhibition of dose-response curves by bumetanide was much greater in SHR than in Wistar Kyoto (WKY) normotensive rats. The expression levels of nkcc1 mRNA and of NKCC1 protein in aortae and heart tissues were higher in SHR than in WKY. Nkcc1 gene promoter was hypomethylated in aortae and heart than those of WKY. These results suggest that promoter hypomethylation upregulates the NKCC1 expression in aortae and heart of SHR.